WO2003091716A1

WO2003091716A1 - Goniometer sample holder with ball and socket joint for aligning a sample to a radiation beam

Info

Publication number: WO2003091716A1
Application number: PCT/GB2003/001805
Authority: WO
Inventors: Steven Buffey
Original assignee: Science and Technology Facilities Council
Current assignee: Science and Technology Facilities Council
Priority date: 2002-04-26
Filing date: 2003-04-28
Publication date: 2003-11-06
Anticipated expiration: 2004-10-26
Also published as: AU2003222987A1; GB0209558D0

Abstract

A goniometer sample holder for aligning a sample to a radiation beam. The sample holder is rotatable about a first axis. An arm having a longitudinal axis provides a sample mount and is pivotally connected to a support by a ball and socket joint so as to allow angular displacement of the longitudinal axis in at least two planes. This permits relatively easy and rapid alignment of the sample to the beam.

Description

GONIOMETER SAMPLE HOLDER WITH BALL AND SOCKET JOINT FOR ALIGNING

A SAMPLE TO A RADIATION BEAM

The present invention relates to a goniometer sample holder and particularly, but not exclusively, to such a holder for an X-ray diffraction goniometer.

A goniometer system is used in the structural analysis of crystalline material by X-ray diffraction. It comprises an X-ray source that is used to direct X-ray beams at a samplb to be analysed and a detector for capturing diffracted X-ray beams that are reflected from the sample. The sample is supported on a holder (often referred to as a "goniometer head") that maintains it in the incident X-ray, beam and enables it to be rotated about itself during the exposure to the beam.

The sample is typically held on the end of a pin mounted on the holder. Prior to analysis it is necessary to position the sample correctly so that during rotation it will not move out of the X-ray beam. Positioning of the sample on the end of the pin is not precise and generally the sample will be offset from the longitudinal axis of the pin so that adjustment is required to ensure rotation about an axis of the sample rather than the pin. With improving data acquisition rates, the time spent in aligning the sample is significant in the overall process and thus automation of sample alignment to reduce this time is now of increasing importance.

Commercially available goniometer sample holders comprise a table with mutually perpendicular linear slides for moving the sample in the two axes and a rotary spindle for rotating the table about a third axis (commonly referred to in the art as the "phi" axis). First the table has to be moved to a datum position and then laborious manual adjustment of the position of the linear slides and of the angular position of the spindle is required to ensure correct positioning. A dedicated tool is required for linear slides and adjustment is difficult as access to the goniometer sample holder i.° restricted. It is known to use motorised drives for the positional adjustments but these suffer from drawbacks. Motors are relatively bulky and therefore prevent the detector from being located as close to the sample as desired. Moreover, as the wires from the motors must pass along the rotary spindle, measures must be taken to accommodate rotation thereof without tangling of the wires. Such measures often add to the bulk and complexity of the design. Whilst collimated X-ray beams are conventionally of the order of 200 micrometers square, technology is ^' advancing such that smaller beam sizes are available (of the order of 5 micrometers square). This places increased emphasis on the precision with which the sample can be aligned to the beam.

It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.

According a first aspect of the present invention there is provided a goniometer sample holder for aligning a sample to a radiation beam, the sample holder being rotatable about a first axis and having an arm with a longitudinal axis, the arm having a first end defining a sample mount and a second end that is pivotally connected to a support so as to allow angular displacement of the longitudinal axis in at least two planes.

The arrangement provides for a relatively inexpensive and compact sample holder that allows precise and relatively rapid alignment of a sample to an X-ray or other radiation beam. The compact arrangement lends itself to the use of automated or robotic systems for mounting the sample. The actuator of the present invention can be conveniently positioned so as not to obscure a radiation beam detector or prevent it from being located in close proximity to the goniometer sample holder. The goniometer sample holder can be retrofitted to existing goniometer systems.

Preferably the longitudinal axis of the arm extends substantially coaxially with the first axis.

The arm is ideally connected to the support by a universal joint that may be in the form of a ball and socket connection. In such an embodiment the ball of the connection is disposed on a second end of the arm distal from said first end.

The sample mount may be defined on the end of a pin that forms part of the arm. An actuator may be provided for pivoting the arm about the pivotal connection. Preferably the actuator is operable to push or pull the arm so as to pivot it about the pivotal connection and may comprise a driven member for contact with the arm. The driven member may have a first part for contacting the arm at one location and a second part for contacting the arm at an opposed location. This enables the arm to be pushed or pulled. The driven member may be driven via a motor and lead screw combination.

According to a second aspect of the present invention a goniometer system comprising a sample holder for aligning a sample to a radiation beam, a radiation source for directing the beam toward the sample and a radiation diffraction detector the sample holder being rotatable about a first axis and having an arm with a longitudinal axis, the arm having a first end defining a sample mount and a second end that is pivotally connected to a support so as to allow angular displacement of the longitudinal axis in at least two planes.

The radiation source may be an X-ray source.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of a goniometer system incorporating a goniometer sample holder according to the present invention;

Figure 2 is a close up view of part of an arm of the goniometer sample holder of figure 1; and

Figure 3 is a perspective view of a goniometer system incorporating the present invention.

Referring now to figure 1 of the drawings, the X-ray diffraction goniometer comprises an X-ray collimator 1 that directs a focussed beam of X-rays (represented by dotted line 2) towards an aligned X-ray detector 3. A sample S to be analysed is mounted on a goniometer sample holder (generally indicated by reference numeral 4) interposed between the collimator 1 and the detector 3 such that the sample is disposed in the beam path 2. The diffracted X-ray beam received by the detector 3 is analysed to determine the structure of the sample.

The goniometer sample holder 4 is supported on the end of a conventional spindle 5 that is rotatable and translatable about its longitudinal (phi) axis by means of remote drive units such as stepper motors (not shown). Disposed above holder 4 there is a camera 6 for remote viewing of the sample S and a cryo-rube 7 that directs a jet of nitrogen at the sample to maintain it at a predetermined cold temperature.

The goniometer sample holder (shown in detail in figure 2) comprises a predominantly cylindrical arm 10, one end 11 of which tapers inwardly and terminates in a spherical member 12 and the other end of which provides a magnetic mount 13 for a pin 14 (referred to as a cryo pin). The sample S (not shown in figure 2) is mounted in a conventional manner on the tip 15 of the pin 14. The spherical member 12 is received in a complementary socket 16 of the spindle 5 to form a ball and socket joint that allows angular displacement of the longitudinal axis of the arm 10 relative to that of the spindle 5. The joint is designed to be sufficiently stiff to prevent any relative movement or "play" of the arm 10 relative to the spindle 5 during rotation of the spindle 5 but sufficiently free of friction to allow easy adjustment of the angle of inclination of the longitudinal axis. The angular displacement is shown schematically in figure 1 by arrows A. The amount of angular movement depicted is exaggerated to assist in understanding.

A remotely operated actuator 17 for automated angular adjustment of the goniometer sample holder 4 is disposed adjacent thereto. The actuator 17 comprises a stepper motor driven lead screw 18 that in turn moves a blade 19 into abutment with the arm 10 so as effect adjustment. The blade 19 is moved in a direction perpendicular to the longitudinal axis of the arm 10 of the holder 4. Operation of the actuator 17 is remotely controlled via a computer (not shown).

In order to align the sample S correctly to the X-ray beam it is viewed on a screen (not shown in the drawings) that displays a magnified image transmitted by the camera 6. The X-ray beam is typically around 200 micrometers square although smaller beams are available. The beam area is marked on the screen by capturing an image of the beam on a film and rotating the film to face the camera. The objective of the alignment process is to ensure that the sample S does not move out of the X-ray beam during rotation of the spindle 5 and this is achieved by ensuring that the image of the sample on screen is maintained within the marked beam area as the spindle 5 is rotated. First the spindle 5 is translated along its longitudinal axis to bring the sample S approximately into the beam path. The camera 6 has a relatively narrow depth of field and the image of the sample is likely to be out of focus at this stage. To correct this the. spindle 5 and goniometer sample holder 4 are moved closer to the camera 6. Once the sample is in focus, the angular position of the arm 10 axis is adjusted, if necessary, by sending instructions to the actuator 17 to move. This has the effect of translating the sample S along the axis of the beam to ensure it is approximately central therewith. The angular movement is so small as to have a negligible effect on the position of the sample S in a direction transverse to the beam and allows translation in increments of around 1 micron along the axis of the beam. The spindle 5 is then rotated through 90 degrees carrying the arm and sample with it, whereupon the angular position of the arm 10 axis is again adjusted. These steps are repeated until the operator is satisfied that rotation of the spindle 5 will not cause the sample to translate out of the X-ray beam.

If necessary, some of the initial coarse adjustment of the goniometer arm 10 may be made manually before fine adjustments are made by remote control of the actuator 17. The arm design allows such manual adjustments to be performed without the need for dedicated tools.

The present invention provides for a relatively inexpensive and compact sample holder that allows precise and relatively rapid alignment of a sample to an X- ray beam. The adjustment process can be easily automated without mounting motors or other drive units directly to the goniometer sample holder. Moreover, the process can be initiated from any position of the arm without the need to set the holder at a datum position in relation to the spindle. The compact arrangement lends itself to the use of automated or robotic systems for mounting the sample. The actuator of the present invention can be conveniently positioned so as not to obscure the beam detector or prevent it from being located in close proximity to the goniometer sample holder. The goniometer sample holder can be retrofitted to existing goniometer systems.

It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. For example, the ball and socket joint of the arm may be spring loaded to ensure that it does not wobble whilst_, still allowing easy adjustment when moved manually or by an actuator. An example of such a spring loaded joint is schematically illustrated in Figure 4. A compression spring 20 biases a piston 21 into contact with the spherical member 12. The piston has a concave indentation 22 to match the curvature of the spherical portion 12. The spring and piston thus provide a biasing force to ensure good frictional contact between the spherical member 12 and the spherical socket 16.

It will be appreciated that the joint need not necessarily be a spherical joint, for instance the joint may be constructed to allow movement in a limited number of directions, for instance in two orthogonal directions only.

The blade 19 may take a variety of forms and may be replaced by a member which contacts the arm 10 at diametrically opposed locations so as to permit the arm to be pushed or pulled and thereby eliminate the requirement to rotate the spindle through 180° in order to move the arm in opposite directions along the axis of the beam. A first example of such an arrangement is illustrated in Figure 5. Here the blade described above is replaced by a member 23 which effectively embraces the arm 10 and supports opposing blades 19a and 19b. Movement of the feed screw 18 (driven by motor/gearbox 24) in a first direction would bring the blade 19a into contact with, the arm 10 to push the arm in the manner of the blade 19 of the embodiment described above. Movement of the feed screw 18 in the opposite direction will bring the second blade 19b into contact with the arm 10 to move (pull) it in the opposite direction.

A second example of a "push/pull" actuator is illustrated in Figure 6. This is very similar to the embodiment illustrated in Figure 5 but differs in that the support member 25 defines a V shape recess 26 and the actuator is mounted on a jack motor 27 for raising and lowering the actuator and thus support 25. By appropriate operation of the jack moto_ 27 the support 25 can be positioned so that surfaces 26a/26b of the N shaped recess 26 lie on the radius of the arm 10. The axis of the arm 10 can then be initially aligned with the axis of the spindle 5 simply by rotating the spindle (and thus arm) through 360°. Whilst not essential, this initial alignment might be desirable.

It will also be appreciated that the actuator may take a variety of forms and need not be the stepper motor/feed screw^' arrangement illustrated. In particular, the actuator could be a robot arm. The various blade arrangements described above could be part of a tool to be picked up and manipulated by a robot arm to automate the alignment procedures of the goniarm 10. This is a further significant advantage of the present invention over the prior art. Other possible modificiations and applications of the invention will be readily apparent to the appropriately skilled person.

Claims

10CLAIMS

1. A goniometer sample holder for aligning a sample to a radiation beam, the sample holder being rotatable about a first axis and having an arm with a longitudinal axis, the arm having a first end defining a sample mount and a second end that is pivotally connected to a support so as to allow angular displacement of the longitudinal axis in at least two planes.

2. A goniometer sample holder according to claim 1, wherein the longitudinal axis of the arm extends substantially coaxially with the first axis.

3. A goniometer sample holder according to claim 1 or 2, wherein the arm is connected to the support by a universal joint.

4. A goniometer sample holder according to claim 3, wherein the universal joint is a ball and socket connection.

5. A goniometer sample holder according to claim 4, wherein the ball of the connection is disposed on a second end of the arm distal from said first end.

6. A goniometer sample holder according to claim any preceding claim, wherein the sample mount is defined on the end of a pin that forms part of the arm.

7. A goniometer sample holder according to any preceding claim, wherein there is provided an actuator for pivoting the arm about the pivotal connection. 11

8. A goniometer sample holder according to claim 7, wherein the actuator is operable to push or pull the arm so as to pivot it about the pivotal connection.

9. A goniometer sample holder according to claim 7 or 8, wherein the actuator comprises a driven member for contact with the arm.

10. A goniometer sample holder according to claim 9, wherein the driven member has a first part for contacting the arm at one location and a second part for contacting the arm at an opposed location.

11. A goniometer sample holder according to claim 9 or 10, wherein the driven member is driven via a motor and lead screw combination.

12. A goniometer system comprising a sample holder according to any preceding claim, and further comprising a radiation source for directing a radiation beam toward the sample and a radiation diffraction detector.

13. A goniometer system according to claim 12, wherein the radiation source is an X-ray source.

14. A goniometer system according to claim 12 or 13, further comprising a camera directed at said sample holder and a display screen for projecting an image of the sample.

15. A goniometer system according to claim 14, wherein there is provided an image representing the radiation beam on the screen.